1. Field of the Invention
The present invention relates to a charge deflection type continuous inkjet printer using water-based ink.
2. Description of Related Art
A conventional continuous inkjet printer has an inkjet head provided with a plurality of nozzles arranged in a single row. The inkjet head continuously ejects ink particles from the nozzles at a frequency of about 100 kHz. In a printing process for forming images on a printing medium, such as paper, which is placed in opposition to the nozzles, an electrical charge is applied to ink particles not to be printed, enabling the ink particles to be deflected and collected. On the other hand, an electrical charge is not applied to ink particles to be used in printing the images, allowing these particles to be deposited onto the printing medium.
When forming a straight line that extends parallel with the nozzle row using the continuous print head, however, the end portions of the line become unstable due to the effects of the electrical charges. More specifically, the end portions of the line are affected by an electric field applied to neighboring ink particle designated for collection. This effect causes the ink particles in the end portions to be deflected slightly during their flight. Contrarily, the center portion of the line is not affected by these electrical charges. Accordingly, ink particles in the end portions of the line fall behind those in the center portion, forming slender whisker-like deviations off the straight line.
Thus, when printing a straight line along the nozzle row direction of the print head, an electrical charge applied to ink particles at the ends of the line that are not to be printed affects neighboring ink particles intended for printing, causing the latter particles to shift slightly from their intended printing positions toward the electrical charge. This effect results in a printing phenomenon in which one or two ink particles on the ends of the line deviate from the straight line, thereby degrading the quality of printing.
The above-described problem occurs also when printing characters. Deviations invariably appear at the ends of the lines in the characters at points where the printed line portions meet unprinted portions. The resulting shape of the printed character becomes different from that of the desired original font.
In view of the foregoing, it is an object of the present invention to provide an improved continuous inkjet printer and an improved continuous inkjet printing method that is capable of eliminating the above-described degradation in printing quality.
In order to attain the above and other objects, the present invention provides a continuous inkjet printer, comprising a continuous print head, a conveying unit, a deflecting unit, a judging unit, and a control data producing unit. The continuous print head has a row of ejection nozzles. The row of ejection nozzles includes a plurality of ejection nozzles which are arranged to be located at a plurality of nozzle positions defined along a first predetermined direction. The row of ejection nozzles is located at a predetermined position along a second predetermined direction that is substantially perpendicular to the first predetermined direction. Each ejection nozzle ejects successive ink particles continuously in a third predetermined direction that is substantially perpendicular to both of the first and second predetermined directions thereby allowing the ejection nozzle row to eject successive rows of ink particles continuously in the third predetermined direction. The conveying unit conveys a printing medium relative to the continuous print head in the second predetermined direction. The deflecting unit receives successive groups or control data, and selectively deflects the ink particles in the successive ink particle rows, based an the received successive control data groups, thereby selectively preventing the ink particles from reaching the printing medium. The judging unit receives a print data group for one of the successive ink particle rows, and judges whether or not the print data group includes straight-line-end data indicative of an end portion of a straight-line that extends in the first predetermined direction. The control data producing unit produces, when the print data group is judged to include the straight-line-end data at some nozzle position, deflection control data for deflecting an ink particle at the subject nozzle position in the subject ink particle row and produces first non-deflection control data for failing to deflect a first ink particle at the subject nozzle position in a first ink particle row that is different from the subject ink particle row.
According to another aspect, the present invention provides a method of printing a straight line with the continuous inkjet printer. The method comprises the steps of: receiving a print data group for one of the successive ink particle rows; judging whether or not the print data group includes straight-line-end data indicative of an end portion of a straight-line that extends in the first predetermined direction; and producing, when the print data group is judged to include the straight-line-end data at some nozzle position, deflection control data for deflecting an ink particle at the subject nozzle position in the subject ink particle row and producing first non-deflection control data for failing to deflect a first ink particle at the subject nozzle position in a first ink particle row that is different from the subject ink particle row.